Portable communication devices, such as cellular telephones, personal digital assistants (PDAs), WiFi transceivers, and other communication devices transmit and receive communication signal at various frequencies that correspond to different communication bands and at varying power levels. A typical receiver in one of these communication devices must be capable of receiving, amplifying, downconverting and extracting useful information from the received signal. The signal received by these devices is typically very weak and is usually amplified prior to subsequent processing. Such an amplifier is referred to as a low noise amplifier (LNA) and is typically implemented to contribute little noise, to provide flat gain and to provide good input and output return loss and linearity.
In a multiple receive band system a single LNA can be implemented for each receive band to meet noise figure requirements for the multiple receive frequencies. Unfortunately, implementing multiple LNAs for multiple receive bands is costly, consumes valuable area on the semiconductor die, and often leads to signal degradation.
Alternatively, a single LNA can be implemented to cover multiple receive frequencies, but such an implementation must use resistive feedback to maintain an acceptable noise figure. Unfortunately, at some frequencies, resistive feedback degrades reverse isolation, degrades return loss, and increases the noise figure.
Therefore, it is desirable to have a receiver that implements a single LNA that overcomes the limitations described above.